1. Field of the Invention
The present invention relates to a vacuum pump system including a vacuum pump with brushless, multi-phase, synchronous motor with a permanently magnetically excited rotor, a control unit for controlling the vacuum pump and including a drive microcontroller and a final stage, and a further microcontroller for monitoring a rotational speed of the motor.
2. Description of the Prior Art
In the past years, brushless motors with a permanently magnetically excited rotor and a shaft having a high rotational speed, found wide application as drives for vacuum pumps. To these pumps belong, e.g., turbomolecular pumps disclosed in German Publication DE-0S 103 31 932. The danger with these pumps lies in the high energy that is stored in the rotor. If this energy is released as a result of pump malfunction, i.e., in the environment, it can cause big damages. Therefore, the housings of the vacuum pump are so formed that they can absorb a substantial amount of the releasable energy. Generally, the energy, which is stored in the rotor, depends on the rotational speed of the rotor. In order to limit the maximum stored energy, the rotational speed should be limited to a highest permissible value. This rotational speed limitation must be insured even when the control electronics of the motor itself malfunctions. The rotational speed limitation also should include protection against an excessive rotational speed.
German Publication DE-0S 102 15 896 suggests to provide in the vacuum pump, in addition to a microcontroller that directly assumes the functions of the motor electronics, a second microcontroller which, in addition to its other functions, monitors the first microcontroller. The drawback of this solution consists in that a large number of components needs to be provided on and in the vacuum pump. The arrangement of highly integrated electronic components on the pump itself might not be possible in many cases, e.g., in an environment with an intensive radiation. In addition, both microcontrollers depend for their operation on only one sensor that senses the rotation of the rotor, which limits the protection against malfunction. Furthermore, the division of the electronics between the vacuum pump and control electronics can lead to the limitation of exchangeability of the electronics and the vacuum pump, i.e., the vacuum pump and the electronics cannot be arbitrarily combined because, e.g., the functional features (e.g., the based code) of the microcontrollers should be adapted to each other. This is not user-friendly and is associated with increased costs.
Accordingly, an object of the present invention is a vacuum pump system in which arbitrary combination of a vacuum pump and control electronics is possible and a reliable overspeed protection is insured.